Lighting a film or television scene is a highly complex process. Lighting technicians must balance many considerations in building an appropriate lighting configuration for a film or television scene. Key considerations include managing tight on-set space and power constraints, avoiding flicker when filming, providing adequate adjustability of color temperature and hue of light, managing budget constraints, and maximizing the efficiency and portability of the light source.
Historically, lighting technicians have relied upon incandescent (e.g., tungsten-halogen), fluorescent, and arclight instruments (collectively, referred to herein as “historical” lighting systems). These historical lighting systems can hinder production teams as a result of their high energy requirements, size, and lack of versatility. Therefore, in order for these lighting systems to be run, large power conversion devices may be required, increasing costs and decreasing ease of use. Furthermore, these historical lighting systems may require dimming devices and other accessories in order for the lights' color, quality, or intensity to be adjusted. As a result, historical lighting systems have remained cumbersome, costly, and difficult to set up.
Additionally, when lighting a subject for a film, television, or other type of photographic shoot, a lighting technician faces the challenge of matching or replicating a specific color temperature or light hue. Historical lighting system solutions require the installation of consumable gel media or the swap of bulb in order to adjust color temperature. Not only are these methods slow and inefficient but they do not allow for continuous adjustability throughout the range of colors. Historical lighting systems also suffer from color temperature drifts as a result of dimming, ambient temperature changes, bulb life, gel media quality, or other conditional changes.
Another method of controlling the intensity and brightness of these historical lighting systems is by attenuation. Attenuating a historical lighting source is typically achieved through the reduction of the voltage flowing through the lamp, which thereby reduces the total amount of energy passing through the filament and light produced.
More recently, solid state lighting has begun to be used for these applications. Solid state lighting systems are generally comprised of semiconductors or semiconducting elements. Solid state lighting solutions provide lower total costs, less bulk, and increased efficiency. However, solid state lighting is not without its drawbacks.
For one, in some circumstances, lighting technicians have simply attempted to create retrofit systems, which involved replacing incandescent, halogen, or arclight light sources with standard high-output class LED lights. Although the light source, such as the bulb, may be solid state, the overall design of the rest of the light remains unchanged. These retrofit systems often lack any novel improvements since fundamentally the light system functions the same as with a historical light source. Since the thermal design and optical system remains unchanged, color renditions can lack accuracy and richness, and color rendering index (CRI) values that are as low as consumer level LEDs. As a result, many of these lights also are susceptible to flickering when used in film and television settings.
Non-retrofit solid state lighting systems often cost more to design and build as a result of the classical method of combining emitters on the same substrate or frame, which involves arranging emitters of two different color temperatures and alternating them in either a “candy stripe” or “checkerboard” pattern along the lighting instrument. These emitter arrangements alternate color temperature every other emitter or every other row. For example, U.S. Pat. No. 8,506,125 B2 (“the '125 patent”) claims an illumination system consisting of “two groups of semiconductor light elements each individually emitting light in a daylight or tungsten color temperature range.” In the '125 patent, checkerboard and striped patterns are discussed as a means of integrating “a plurality of semiconductor light elements.” One notable problem particular to checkerboard patterns is that it is not possible to cleanly integrate resistors because the emitter density is uniform throughout and there is no natural space left for any of these features. It also is more difficult to route signal traces on the printed circuit board since the common neighbors do not exist.
As stated above, solid state lighting sources conduct, and therefore emit light, only when fed a specific voltage or very narrow range of voltages. Variance of only a few hundredths of a volt up or down from that design voltage will result in interrupted electron flow and therefore no light emission. Other solid state lighting semiconductors and alternative light emission technologies have this same narrow voltage range of operation. The fixed forward voltage of solid state lighting elements presents a few unique challenges when it comes to attenuating their output levels and maintaining their stability.
For instance, current solid state lighting systems exhibit negative effects when attempting to change color temperature or intensity, crucial capabilities to meet the demands of today's production teams. When changing color temperature, other solid state lighting systems lose significant output while also changing the shape and quality of light that is output. When this happens, shadows tend to fall differently on lit subjects, requiring technicians to have to further adjust the lighting for the scene. Additionally, current solid state lighting systems do not have discrete and precise control of the intensity of the lighting system, which hampers the ability of production teams to properly light scenes.
Currently, there are two accepted methods for attenuating the output levels of a solid state lighting source: current control and pulse width modulation. Current control is the simple regulation of current flowing through emitter clusters or other solid state light emission devices. While this is similar in effect as the reduction in voltage involved in the attenuation of a classical light source as discussed above, the voltage in this case remains constant in order to satisfy the forward voltage requirement, but the reduction in current results in reduced light output. Current control inherently results in relatively flicker free performance and reasonably stable light output, but such designs require large passive components to filter out ripple effects due to current regulation. Furthermore, it also results in color shifts and a lack of precision control below 10% of the emission device's standard current consumption. Often times, specialized and expensive regulation is required below the 10% threshold and the color results are still greatly compromised.
The other accepted method of attenuating solid state lighting output is Pulse Width Modulation (“PWM”). It functions by rapidly switching emitter(s) on and off in a cyclic manner, thereby reducing light output as perceived by a human eye, sensor, video camera, film emulsion, or other recording or measuring device. The longer a percentage of time the emitter is on and making light, the brighter the average illuminance appears. If this switching is sufficiently rapid, the human eye cannot see the flashing but perceives a reduced brightness because the brain “smoothes out” the rapid flashes. The frequency at which this begins to occur is at least 20-30 Hz, just like a television or motion picture projector. However, when photographing emitters that are dimmed using this technique, the film or digital camera can perceive the switching and the result is a “temporal artifact” which looks like banding, partially exposed frames, or an entire bank of emitters that appear off. These artifacts are caused by the shutter of the camera being in transition from open to closed or closed to open during a time when the emitters are in their off state of the pulse-width cycle.
Conventionally, the industry approach to solving this problem involved speeding up the switching frequency. By increasing the switching speed to a few thousand times per second (greater than 1 kHz) most cameras operating at normal shutter speeds can no longer discern the pulsing and instead see a smoothed, but attenuated, average intensity just like the human eye. However, this higher switching frequency results in a higher complexity design and the need for more expensive transistors or other switching devices. Additionally this technique is limited to only the most basic of photographic application because many advanced cameras run at many various shutter speeds, effectively nullifying the gains resulting from the higher switching frequency. For instance, a high speed camera would still discern flicker. Increase the switching frequency even more and the problem still occurs even at some minute level. Non-global shutters further complicate the matter by sampling (or exposing, in photographic terms) pixels in stripes or segments of the final image instead of sampling the entire frame at once.
PWM has another limit, at very high switching frequencies (greater than 1 MHz), which could be flicker free in photography even at very high frame rates, the switching transistors have to be incredibly specialized types used in radio transmission. Therefore, the very act of switching these transistors on and off at these high frequencies result in radio emissions. Thus, there is an upper speed limit of practical PWM.
In addition to suffering from flicker and the difficulty of attenuating the light source, existing solid state light instruments can only function as a single sized stand-alone instrument, and do not scale in any way. This lack of modularity limits the usage of any one particular lighting instrument. The only way for these panels to appear as if they provide a single larger light source is to put them on separate stands, rigs, or bracketry and place them next to each other. However, each instrument is then controlled and operated as a separate device and requires numerous accessories in order to be positioned in a way that makes them appear to be a single light source. For instance, US Pat. Appl. No. 20130099669 A1 (“the '669 application”) discloses a method in which different lighting instruments can be grouped together on a network and manipulated as one light source. This makes uniform lighting adjustments much easier, but since the lights lose their individual identification on the network, the user is forced to manipulate them all as one unit which eliminates the added flexibility and control of light accuracy.
Furthermore, existing solid state lighting instruments are designed and manufactured in a way that make repairs and upgrades very difficult for consumers. Repairing burnt out or malfunctioning emitters require the consumer to send the light back to the manufacturer or requires a specialist to be sent onsite and repair or replace any malfunctioning elements of the light. This creates a major issue for users, who end up losing money when they are not able to rent or use equipment during repair time. Another problem with this approach to manufacturing is that users cannot upgrade the emitters, microprocessors or firmware when they become outdated.